ISO 4126-10:2024 過度の圧力から保護するための安全装置 | ページ 6

3.1.1

加圧システム

安全装置によって過剰な圧力の蓄積から機器が保護されている

3.1.2

臨界充填閾値

ϕ_限界

サイジング条件での 加圧システム (3.1.1) 内の最大初期液体充填閾値 (液体ホールドアップ)、蒸気の解放が発生し、単相ガスまたは蒸気の流れが予想されるwhere の値

注記 1:臨界充填閾値は、システムの総体積の比率として表されます。

注記 2:臨界充填閾値を超える充填レベルでは、二相流が発生すると想定されます。

3.1.3

初期液体充填レベル

ϕ0_​

サイジング条件における 加圧システム (3.1.1) 内の液体ホールドアップ

注記 1:初期の液体充填レベルは、システムの総体積の比率として表されます。

3.1.4

インレットライン

加圧システム (3.1.1) を安全装置入口に接続する配管および関連継手

3.1.5

アウトレットライン

安全装置の出口を格納システムまたは大気に接続する配管および関連継手

3.1.6

ベントラインシステム

安全装置、 入口ライン (3.1.4) と 出口ライン (3.1.5) の組み合わせ

3.1.7

極低温容器

液化ガスを含む低温での用途を目的とした真空ジャケット付き容器

3.2.1

maximum allowable working pressure

p_MAW

maximum pressure permissible at the top of a pressurized system (3.1.1) in its operating position for designated temperature

3.2.2

maximum allowable accumulated pressure

p_MAA

sum of the maximum allowable working pressure (3.2.1) and the maximum allowable accumulation (3.2.3)

Note 1 to entry: The maximum allowable accumulation is established by applicable code for operating and fire contingencies.

3.2.3

maximum allowable accumulation

Δp_MAA

pressure increase over the maximum allowable working pressure (3.2.1) of a pressurized system (3.1.1) during discharge through the safety device

Note 1 to entry: The maximum allowable accumulation is expressed in pressure units or as a percentage of the maximum allowable working pressure.

3.2.4

opening pressure

p_open

predetermined absolute pressure at which a safety valve under operating conditions at the latest commences to open

3.2.5

absolute overpressure

Δp_over

pressure increase over the opening pressure (3.2.4) , p_open, of the safety device

Note 1 to entry: The maximum absolute overpressure is the same as the maximum accumulation, Δp_MAA, when the opening pressure of the safety valve is set at the maximum allowable working pressure (3.2.1) of the pressurized system (3.1.1) .

Note 2 to entry: The absolute overpressure is expressed in pressure units or as a percentage of the opening pressure.

3.2.6

overpressure

p_over

maximum pressure in the pressurized system (3.1.1) during relief, i.e. pressure less or equal to the maximum accumulated pressure

3.2.7

sizing pressure

p₀

pressure at which all property data, especially the compressibility coefficient, ω, are calculated for sizing the safety device

Note 1 to entry: In the case of tempered and hybrid reactive systems, the sizing pressure shall be as low as reasonable possible, but should not affect the normal operation. In the case of non-reactive and gassy systems (3.5.3) , the designer may choose a higher value for the sizing pressure, but it shall not exceed the maximum allowable accumulated pressure (3.2.2) .

3.2.8

critical pressure

p_crit

fluid-dynamic critical pressure occurring in the narrowest flow cross-section of the safety valve and/or at an area enlargement in the outlet line (3.1.5)

Note 1 to entry: At this pressure, the mass flow rate approaches a maximum at a given sizing condition in the pressurized system (3.1.1) . Any further decrease of the downstream pressure does not increase the flow rate further. Usually, the critical pressure occurs in the safety valve, either in the valve seat, inlet nozzle and/or valve body. In the bursting disc, critical pressure can occur downstream of the device at a minimum flow area, at the exit of the vessel or a change in pipe diameter. In long safety device outlet lines, multiple critical pressures can also occur.

3.2.9

stagnation condition

condition when fluid is at rest

3.2.10

critical pressure ratio

η_crit

ratio of critical pressure (3.2.8) to the sizing pressure (3.2.7)

3.2.11

thermodynamic critical pressure

p_c

state property, together with thermodynamic critical temperature (3.6.1) , at the thermodynamic critical point

3.2.12

back pressure

p_b

pressure that exists at the outlet of a safety device as a result of pressure in the discharge system

Note 1 to entry: Back pressure can be either constant or variable; it is the sum of superimposed and built-up back pressure (3.2.13) .

3.2.13

built-up back pressure

pressure existing at the outlet of the safety device caused by flow through the valve or bursting disc and discharge system

3.2.14

inlet pressure loss

Δp_loss

irrecoverable pressure decrease due to flow in the piping from the equipment that is protected to the inlet of the safety device

3.2.15

blowdown

Δp_BD

difference between opening pressure (3.2.4) and reseating pressure of a safety valve

Note 1 to entry: Blowdown is normally stated as a percentage of the opening pressure.

3.2.16

dimensionless reduced pressure

p_red

local pressure divided by the thermodynamic critical pressure (3.2.11) of the substance

3.3.1

mass flow rate required to be discharged from a pressurized system

Q_m,out

mass flow rate required to avoid that the pressure exceeds the maximum allowable accumulated pressure (3.2.2) in the pressurized system (3.1.1) during relief

3.3.2

feed mass flow rate into the pressurized system

Q_m,feed

maximum mass flow rate through a feed line or control valve fed into the pressurized system (3.1.1) being protected

3.3.3

dischargeable mass flux through the safety device

mass flow rate per area through a safety device at the sizing conditions calculated by means of the certified discharge coefficients for gas and liquid flow

Note 1 to entry: See Formula (48).

3.3.4

certified valve discharge coefficient for single-phase gas/vapour respectively liquid flow

K_dr,g 〈gas〉

K_dr,l 〈liquid〉

correction factor defined by the ratio of the theoretically dischargeable mass flux through the safety device (3.3.3) to an experimentally determined mass flux through a device of the same manufacturer's type

Note 1 to entry: The discharge coefficient of a safety valve is related to the valve seat cross-section and accounts for the imperfection of flow through the device compared to that through a reference model (ideal nozzle). Certified values for gas and liquid flow, K_d, are usually supplied by valve manufacturers or determined by experiment. Rated discharge coefficients K_dr, equal to 0,9 K_d, are used to calculate the safety valve sizing area.

Note 2 to entry: The discharge coefficient of a bursting disc is related to the disc cross-section and accounts for the imperfection of flow through the device compared to that through a reference model.

3.4.1

safety device sizing area

A₀

most essential result of the sizing procedure in accordance with this document required to select an adequately sized safety device and defined as the minimum cross-section of flow area

Note 1 to entry: It is important that the dischargeable mass flux through the safety device (3.3.3) be related to this specific area.

3.4.2

effective flow area of the feed line or the control valve

A_feed

discharge flow area of a feed line or control valve in the line to the pressurized system (3.1.1)

3.5.1

gas/liquid mixture

fluid mixture composed of both a liquid part and a gas part, in which the gas is not necessarily of the same chemical composition as the liquid

3.5.2

tempered system

fluid system in which some energy is removed from the liquid phase by evaporation or flashing

3.5.3

gassy system

fluid system in which permanent gas is generated (e.g. by chemical reaction or by evolution from solution) and in which no significant amount of energy is removed from the liquid by evaporation at the sizing conditions

3.5.4

hybrid system

fluid system that exhibits characteristics of both tempered and gassy systems (3.5.3) to a significant extent at the sizing conditions

3.5.5

thermal runaway reaction

uncontrolled or undesired exothermic chemical reaction

3.6.1

thermodynamic critical temperature

T_c

state property, together with thermodynamic critical pressure (3.2.11) , at the thermodynamic critical point

3.6.2

sizing temperature

T₀

temperature of the pressurized system (3.1.1) at the sizing conditions

3.6.3

overtemperature

T_over

maximum temperature in the pressurized system (3.1.1) during relief

3.6.4

saturation temperature difference

ΔT_over

difference between the saturation temperature at the maximum pressure during relief, p_over, and the saturation temperature at the sizing pressure (3.2.7) , p₀

3.6.5

dimensionless reduced temperature

T_red

local temperature divided by the thermodynamic critical temperature (3.6.1) of the substance